French Patent Application Publication No. FR 2 733 142 discloses a device for measuring elasticity that realizes a measuring in 2 dimensions but is also suitable for realizing measurements in three dimensions. However, this device does not comprise a scanning means suitable for performing the scanning with the bar or bars in two perpendicular directions.
U.S. Pat. Nos. 6,176,827; 5,099,848; 6,277,074 and 5,474,070 and US Patent Application Publication No. 2002/0001098 disclose solutions for making only one measurement in two dimensions, at times with a fixed bar.
At the present time no ultrasonic devices for measuring the elasticity and allowing this measuring to be viewed in two or three dimensions are commercially available.
Furthermore, as concerns the measuring of elasticity in two dimensions, the article “Shear Modulus Imaging with 2D Transient Elastography” by L. Sandrin, M. Tanter, S. Catheline and M. Fink in Ultrason. Ferroelectr. Freq. Control, vol. 49 (4), pp. 426-435 (2002) is known and describes a technique for measuring elasticity and a representation in two dimensions of this measuring. The resolution of the inverse problem, that is to say, going back to the parameters that describe the viscoelastic environment to be measured, is imperfect here because the displacement is not known in the three spatial directions. In fact, according to the computational algorithms connected to the measurements carried out by the device presented in that article, the operators are obliged to formulate hypotheses to resolve the calculations of elasticity, but practice has demonstrated that these hypotheses are seldom justified.
WO 00/70362 discloses a system using magnetic resonance elastography (ERM), in which a viscoelastic zone (such as the human chest) is excited by mechanical waves. The subject matter of that invention is based on the hypothesis that the results of the measurements by ERM are solutions independent of the time of the partial differential equations precisely describing the behavior of mechanical waves in a viscoelastic material (including for longitudinal waves and in a reflecting environment). To this end the Young module contained in these equations can be calculated. In addition, it proposes using (in a predominant manner) longitudinal waves, that are capable of penetrating into the human chest, which is not the case for transversal waves. In that device, obtaining the elasticity map requires much time. Furthermore, the cost of implementing that device is very high.
French Patent Application Publication No. FR 2 791 136 discloses an imaging process for observing the propagation of an impulsive wave of low-frequency shearing at the same time in a multitude of points of a viscoelastic diffusing environment. To this end ultrasonic compression waves are emitted at an ultrarapid cadence that allows the obtention of a succession of images of the environment. Then, the images obtained are processed in non-real time by intercorrelation to determine at each point of each image the movements of the environment during the propagation of the shearing wave.
That invention is not satisfactory because it requires envisaging two hypotheses: the second derivative of the displacement is considered to be zero in the direction orthogonal to the plane, and the environment is assumed to be perfectly incompressible.